Semiconductor doping involves intentionally introducing impurities into a substrate in order to control its electrical properties. As such, doping methods are very important in the semiconductor industry. However, many of the currently known methods for doping substrates utilize harsh conditions, which may cause irreparable damage. For example, plasma immersion ion implantation is performed by generating a plasma containing ions of species to be implanted in a semiconductor wafer or workpiece. The plasma may be generated using a plasma source such as a toroidal plasma source at the reactor chamber ceiling. Ion energy sufficient to achieve a desired ion implantation depth profile below the wafer surface is provided by coupling a very high RF bias voltage (e.g., 10 kV to 20 kV) to the semiconductor wafer through an insulated cathode electrode within the wafer support pedestal. High implant dose rates require a high plasma ion density, which is achieved using a toroidal plasma source operating at a low chamber pressure. The requisite ion implant depth profile requires a very high ion energy, which is achieved by applying a very high RF bias voltage across the plasma sheath at the wafer surface. The process gas employed in plasma immersion ion implantation can be a fluoride or a hydride of the dopant species to be implanted. Such a process involves harsh conditions, which are not suitable for some types of substrates.
There is therefore a need for gentler methods which do not harm the underlying substrate. Additionally, currently known methods of doping transistors often do not yield the conformal and consistent results that are required, particularly in the area of substrates with a high aspect ratio, such as is found with FinFET transistors. Thus, there is a continuing need for methods and apparatus for effectively doping finFET transistors.